The present invention relates generally to microphone control systems and, more particularly, to an enhancement and refinement of the invention of U.S. Pat. No. 4,658,425, issued to Stephen D. Julstrom and entitled "Microphone Actuation Control System Suitable for Teleconference Systems." U.S. Pat. No. 4,658,425 has the same inventor and is owned by the same entity as the present application.
The contents of U.S. Pat. No. 4,658,425 are incorporated herein by reference, as if fully set forth below. For ease of reference, U.S. Pat. No. 4,658,425 is hereinafter referred to simply as "the previous Julstrom patent."
The automatic microphone control referred to pertains to systems with multiple microphones and is suited for use in sound reinforcement, recording, broadcast, teleconference, and other applications. Only the most appropriate microphone or microphones of a multiple microphone conference pickup system are automatically actuated (brought up to full gain) in response to speech originating within the conference room. Microphones which are not, at some moment, the most optimum ones to pick up the conference room speech are not actuated (remain attenuated or turned off). The control system does not allow speech from the far end of a teleconference emitting from a conference room loudspeaker to actuate the conference room microphones.
The major benefits of keeping the minimum number of microphones actuated at any given time are a minimization of the pickup of room noise and reverberation for clearer sound quality and minimization of the pickup of loudspeaker sound for lessened feedback potential in local reinforcement or teleconference applications. This is discussed more fully in the previous Julstrom patent and in "Direction-Sensitive Gating: A New Approach to Automatic Mixing" by Stephen Julstrom and Thomas Tichy, Journal of the Audio Engineering Society, Vol. 32, Nos. 7/8, July 1984, pp. 490-506.
Generally, the objects of the previous Julstrom patent were to actuate only the most appropriate microphone or microphones for one or a plurality of talkers with maximum sensitivity in the presence of varying background room noise, and to inhibit actuation of microphones for teleconference loudspeaker sound with minimal inhibition of desired microphone actuation for locally originating speech. These objects were generally met by the invention of the previous Julstrom patent. However, two problem areas remained.
The initial application of the previous Julstrom invention was in a modular teleconference system where all microphones were operated at the same electroacoustic sensitivity with presumably acoustically similar local surroundings for each microphone in a system. Under these conditions, unwanted actuation of a second microphone by the reverberant "trail" of speech following the proper actuation of a first, more appropriate microphone was adequately inhibited by the action of the MAX bus, as explained in the previous patent. However, when two or more microphones in a system were operated at significantly different gains in a reverberant environment, the MAX bus alone did not always prevent secondary actuation of a microphone with higher electroacoustic gain. (Electroacoustic gain refers here to the combined effects of microphone sensitivity and the following electrical gain.)
Also, while the previous Julstrom invention properly inhibited microphone actuation for teleconference loudspeaker sound, it also tended to excessively inhibit microphone actuation for local conference room speech occurring simultaneously with loudspeaker sound when strong direct acoustical coupling from the loudspeaker to the microphones was present.